A new technique for uranium enrichment, specifically enrichment of the U.sub.235 isotope, is shown in patent application Ser. No. 25,605, filed Mar. 25, 1970 now U.S. Pat. 3,772,519, and in corresponding French pat. 71.14007, Jan. 10, 1971, specifically incorporated herein by reference. An exemplary system there disclosed operates by generating a vapor of uranium metal which expands as a particle flow. The U.sub.235 isotope is selectively ionized by application of narrow bandwidth precisely tuned laser radiation to selectively excite and ionize the U.sub.235 isotope without substantial ionization of the U.sub.238 isotope or other isotopes. Once ionized, the particles of the U.sub.235 isotope are separated from the plasma by changing their flow direction under the influence of a pulsed electric and continuous magnetic field which produces crossed-field magnetohydrodynamic forces on the ions. The different trajectory of these ions resulting from the crossed-field acceleration permits their collection apart from the remaining constituents of the vapor flow.
If it is desired to use only a magnetic field to separate the selectively ionized particles from the plasma, additional factors must be taken into consideration for an efficient enrichment scheme. In particular, it is desired to use a high density vapor flow in order to increase the quantity of particles which are separated. The increasing density predicts a reduction in the charge exchange time for the selectively ionized particles which, in turn, demands a higher or stronger magnetic field in order to deflect the flowing ions by a substantial angle before they lose their charge and are no longer affected by the magnetic field. A strong magnetic field, however, increases the Zeeman splitting or broadening of the absorption lines for each isotope thereby reducing the efficiency or selectivity of the excitation and ionization produced by the laser radiation.